This program has been directed at elucidating the fundamental mechanisms of action relating to pesticides and other environmental contaminants in several animals species. Studies of the enzymic reactions involved in action, inactivation and interaction of these xenobiotics have been undertaken in order to better understand the molecular toxicology of these compounds. As an essential aid to further elucidation of comparative toxicity at the molecular level, a high resolution stopped flow spectrophotometer is needed to continue the progress already made during the previous year of the project in studying the biochemical characteristics of microsomal enzymes and their interaction with xenobiotics.